A magnetic thin film formed from Permalloy of about 80% Ni and 20% Fe has been widely used as a core of a magnetic thin-film head. A magnetic thin film of this kind is featured in that it performs a high-speed switching operation in the high-frequency region.
A thin film of Permalloy with a magneto-striction constant within the range of .+-.2.times.10.sup.-6 has an anisotropic magnetic field of 3 to 5 Oe, and a saturation magnetic flux density of as high as about 1 T. Therefore, there has been a problem that the film is undesirable to improve the recording density, the structural reliability, and the resolving power of a magnetic head.
Beam and Siegle disclose application of time-sequenced orthogonal fields, at 12, 3, 6 then 9 o'clock, during deposition of Permalloy films for improving and centroling the anisotropy of the films (see IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-1, 1964 pp. 66-67).
When a magnetic thin film having a saturation magnetic flux density larger than that of the Permalloy is developed as a core material of a magnetic thin-film head, the following three advantages are achieved: an increased recording density, an improved structural reliability, and an improved resolving power of the magnetic head.
In order to improve the magnetic properties of the Permalloy, an attempt has been made to increase the saturation magnetic flux density of Permalloy by adding Co as the third element to a Ni-Fe binary alloy which is the base composition of Permalloy.
The above attempt is disclosed in a number of well-known references. For example, Bradly studied the magnetic properties of a thin film of Ni-Co-Fe ternary alloy and found that when the magnetrostriction constant is reduced to zero, the thin film shows a saturation magnetic flux density higher than that of a thin film of Permalloy and that when the amount of Co added exceeds 10% by weight, the anisotropic magnetic field exceeds 10 Oe, and as a result the magnetic permeability decreased (see Journal of Applied Physics, Supplement to Vol. 33 (1962) pp. 1051-1057).
Tolman discloses that when a thin film Ni-Co-Fe ternary alloy having an approximately non-magnetrostriction constant is formed under application of a unidirectional external magnetic field, both its anisotropic magnetic field and coercive force are increased by the amount of Co (see Journal of Applied Physics, Vol. 38 (1967) pp. 3409-3410).
Further, Bozorth discloses that an alloy composition providing a nearly non-magnetostriction constant (i.e. a composition in the range of 0-80% by weight of Ni, 0-90% by weight of Co, and 0-20% by weight cf Fe) had a saturation magnetic flux density larger than that of Permalloy (see, "Ferrromagnetism" 4th edition, published by Van Nostrand, p. 165).
Sakakima discloses that the magnetic permeability of a cobalt-base alloy film was increased by annealing the film, after its formation, under application of a rotating magnetic field (see IEEE Transactions on Magnetics, Vol. Mag-19, 1983, pp. 131-135).